adding flat pileup profiles
Adding two pileup profile files, with a flat mu profile (except for a bit more in the last bin because of the need to have the integer population sum to the mc21/mc23a pileup fractions) between 25-75 and 50-75 respectively. They can hopefully be picked up with a postInclude (need to test that) for MC requests that need a flat pileup profile. They will be ignored by all standard workflows, so the CI won't be affected.